I think that last post is a great way to start. Then maybe you could blend the story of Animal Farm with actual history in Trotsky's life and/or parts of the Russian Revolution. For example, after introducing the comparison, and the metaphors of pigs, state that the story and reality are so similar that the line between has blurred. Then write something like, "Once Snowball was exiled, he began to read Marxism. At first he didn't find it all that persuasive, but gradually he it appealed to him and he combined it with his own form of Animalism. Unfortunately, Stalin, I mean Napoleon, had him exiled. Then Napoleon, a.k.a. Stalin became buddies with Hitler, I mean Mr. Frederick and they played cards, cursed at each other and exploited the workers and were basically a bunch of pigs.
You might think about all the ways in our culture we have personified the pig. We call cops pigs. We call a messy room a pig sty, we call extreme spending by our politicians - pork. Then, transition into your thesis by reminding your reader we make extreme comparisons or use hyperbole in our culture to magnify the importance of an issue. This is exactly what George Orwell set out to do. His allegorical fable Animal Farm purposefully illustrated what we need to understand about the Russian Revolution just as the paper you write will set out to demonstrate what we need to know about Trotsky as readers.
Just an idea. Hope you get a few for comparison's sake.